1. Field of the Invention
This invention relates to a fastener for an electronic component, and more particularly to a fastener when an inductance element such as a surface-mounted-type pulse transformer or the like, which is adapted to be used in a hybrid integrated circuit for, e.g., a digital transmission, is assembled.
2. Description of the Prior Art
The assembling of a surface-mounted-type inductance element of this type is generally performed by preparing a bobbin having a terminal block formed integrally therewith, coiling primary and secondary wires around an axial portion of the bobbin, winding a termination of each of the primary and secondary coils around one of external terminals attached to the terminal block of the bobbin and assembling cores to the bobbin. Unfortunately, in the inductance element assembled in the manner described above, the coils around the bobbin are exposed to the external air, so that when the inductance element is soldered onto a printed circuit board by, for example, reflow-soldering the external terminals to conductive patterns of the printed circuit board, the inductance element will be badly affected by heat required and solder used in the soldering operation. After the inductance element is soldered onto the printed circuit board, it is generally cleaned by a solvent. When the inductance element is cleaned by a solvent, it will also be badly affected by the solvent, since the coils around the bobbin are exposed to the external air as described above. Furthermore, the inductance element in which the coils around the bobbin are exposed to the external air as described above is unable to resist moisture. That is, the inductance element constructed in the manner described above is inferior in heat resistance, solder resistance and moisture resistance. Thus, it is considerably susceptible to an external environment.
In order to overcome the disadvantages of the inductance element, the whole inductance element including the cores may be covered by electrically insulating resin material having heat resistance, with the external terminals being projected outwardly. However, when the whole inductance element including the cores is covered by the electrically insulating resin material, stress associated with hardening of the resin material and stress associated with expansion and contraction of the resin material occurring due to a temperature change may cause the cores to be separated from each other and/or destroy the cores, resulting in the magnetic characteristics of the inductance element significantly deteriorating.
In an effort to overcome the problem of the deterioration of the magnetic characteristics brought about during the assembling of the inductance element, a design, as disclosed in a patent application which was filed in U.S.A. on Apr. 24, 1989 and is now pending in the United States Patent and Trademark Office as application Ser. No. 342,216, was tried. This design comprises a bobbin; windings around the bobbin; external terminals projecting from the bobbin, around each of which external terminals a termination of one of the windings is coiled; a mold covering the bobbin in a manner to allow portions of the external terminals to be projected outwardly from the mold, the mold being formed of resin material having heat resistance and including a base portion covering a substantially lower portion of the bobbin, a step portion covering a substantially middle portion of the bobbin and including a through-hole section covering a surface of a bore of the bobbin, and a top portion covering a substantially upper portion of the bobbin; and a pair of cores assembled to the resin mold in a manner to be inserted at their portions in the through-hole section of the mold and disposed between the top portion and base portion of the resin mold. In U.S. patent application as stated above, it is suggested that after the cores are assembled to the resin mold, the cores are fastened to the resin mold by means of a self-adhering tape or a clip. As clearly seen from FIG. 6 of the drawings accompanying U.S. patent application as stated above, when a self-adhering tape is employed, the self-adhering tape is applied to the cores in a manner to substantially surround the cores and, when a clip is to be employed, a clip of a substantially U-shape is prepared and fitted on the cores in a manner to substantially surround the cores. Each of these conventional fasteners in use may clamp the cores in a manner to cause the cores to come into contact with each other, but can not effectively position the cores with respect to the resin mold because each of these conventional fasteners is designed so as to be applied to the cores only. Therefore, in the case where a size of a mold, a size of a through-hole section of the mold and/or a size of a space between top and base portions of the resin mold vary from inductance element to inductance element, when a pair of cores are assembled to a resin mold of a certain inductance element, any space may be produced between the cores, assembled to the resin mold, and the mold. In this case, when any vibration, shock and/or impact are accidentally applied to the inductance element, even though the cores are clamped by the conventional clip or self-adhering tape, the cores may be jolted by the vibration, shock and impact. Therefore, the inductance elements to which these conventional fasteners are applied are inferior in vibration resistance, shock resistance and impact resistance.
The jolting of cores which may occur, when any vibration, shock and/or impact are accidentally applied to an inductance element having the cores, may be prevented by fixing the cores to a resin mold of the inductance element by means of adhesives. However, in the case where fixing of the cores to the resin mold is performed by bonding the cores to the resin mold by means of adhesives and thereafter the inductance element is cleaned by a solvent, such solvent may bring about dissolving or peeling of the adhesives, resulting in the cores tending to slip off the resin mold. Further, in the case where adhesives are applied to the cores and resin mold, the cores may be badly affected by bonding stress, which will be produced upon applying of the adhesives. Furthermore, stress associated with expansion and contraction of the applied adhesives which will occur due to a temperature change may degrade characteristics of the cores. Therefore, it is undesirable that fixing of cores to a resin mold is carried out using adhesives. Alternatively, the whole inductance element covered by a resin mold, in which cores are clamped by means of the conventional self-adhering tape or clip, may be further covered with a resin mold. However, the inductance element assembled in the manner described above becomes large-sized, so that the inductance element is not suitable for high density mounting of electronic components.